Thank you dooglus for explaining this so clearly! I didn't realize SD allows you to split a single transaction into multiple bets now. From what I understand, there was an update to the Bitcoin network not too long ago that doesn't actually allow you to use the exact same transaction ID twice.

I put up a simple page at http://dooglus.com/sd/ that prompts for the txid and the secret and calculates the magic number(s) for you, if you don't want to install Python for yourself.